Fuel oil treatment

Abstract

An additive comprising an oil-soluble polymer of a C2 to C6 mono-olefin such as polyisobutylene, which polymer has a molecular weight of less than about 500, is used in a fuel oil to reduce, on combustion of the fuel oil, one or more of particulate emissions, hydrocarbon emissions, carbon monoxide emissions, and oxides of nitrogen emissions.

We claim: 
     
       1. A fuel oil composition comprising a major proportion of a middle distillate fuel oil and a 5,000 ppm of an additive consisting essentially of polyisobutylene having a number average molecular weight of 450 (as measured by GPC). 
     
     
       2. The composition of claim 1 wherein the additive is present in combination with 5 to 500 ppm one or more oil-soluble ashless dispersants and/or one or more cetane improvers. 
     
     
       3. The composition of claim 2 wherein one of the dispersants is an oil soluble compound of the formula ##STR4## or mixtures of two or more such compounds, wherein R 1 , R 2  and R 3  may be the same or different and are independently hydrogen or a hydrocarbyl substituent having from 2 to 600 carbon atoms, or a keto, hydroxy, nitro, cyano, or alkoxy derivative thereof, provided that at least one of R 1 , R 2  and R 3  is a hydrocarbyl substituent having from 2 to 600 carbon atoms or said derivative thereof, or wherein R 1  and R 2  together from a hydrocarbylene substituent having 4 to 600 carbon atoms or a keto, hydroxy, nitro, cyano or alkoxy derivative thereof, provided that R 1  and R 2  together with the carbon atom which forms the C--R 1  bond with R 1  and the nitrogen atom which forms the NR--R 2  bond with R 2  form a ring having at least 5 members, wherein Z represents   --R.sup.10 [NR.sup.11 (R.sup.10)].sub.e.sup.-       --[R.sup.10 R.sup.11 N].sub.f R.sup.10 [NR.sup.11 R.sup.10 ].sub.g.sup.-     wherein each R 10 , which may be the same or different, represents an alkylene group having from 1 to 5 carbon atoms in its chain, R 11  represents a hydrogen atom or a hydrocarbyl group, and e is from 0 to 6, f is from 1 to 4, g is from 1 to 4, provided that f+g is at most 5, each R 4  is independently H or an alkyl group having up to 5 carbon atoms, R 5  is an alkylene group having up to 6 carbon atoms in the chain, optionally substituted by one or more hydrocarbyl groups having up to 10 carbon atoms, an acyl group having from 2 to 10 carbon atoms, or a keto, hydroxy, nitro, cyano or alkoxy derivative of a hydrocarbyl group having from 1 to 10 carbon atoms or of an acyl substituted by one or more hydrocarbyl groups having up to 10 carbon atoms, an acyl group having from 2 to 10 carbon atoms, or a keto, hydroxy, nitro, cyano or alkoxy derivative of a hydrocarbyl group having from 1 to 10 carbon atoms or of an acyl group having from 2 to 10 carbon atoms, R 6  is a hydrocarbyl substituent having from 2 to 600 carbon atoms or said derivative thereof, b is from 1 to 6, c is from 1 to 6 and d is from 0 to 12.   
     
     
       4. The composition of claim 2 wherein one of the dispersants is a hydrocarbyl-substituted succinimide or succinamide. 
     
     
       5. The composition of claims 1, 3 or 4 wherein a cetane improver is present as the one or more co-additive.